I'm a new member of this forum. I was diagnosed with NPH in 2008, and had a Medtronics Strata valve with anti-siphon device installed in Jan. 2009 as part of a vp shunt system. It worked well for about 2 years, reset itself once after that, and started siphoning the next year. I had a Miethke Shunt Assistant added on to the system last summer. The darn thing has started siphoning again! My NSG has reset it to a lower flow, but it's not helping. I think I'm going to try to schedule replacement with a different type of valve. Seems like Medtronics needs to do a better job of quality control. It's good to know I'm not alone in this, but it would be better to do away with the headaches and nausea.